U.S. Pat. No. 3,937,349 discloses a crown cap for a bottle having a pull tab thereon which is pulled to separate the cap and remove the cap from the bottle.
G.B. 1,415,466 discloses a cap for a beer keg having a pull tab thereon which is pulled to fracture the skirt of the cap to enable removal of the cap from a beer keg.
U.S. Pat. No. 4,779,750 discloses a cap for a beer keg having a pull tab thereon which is pulled to separate the cap thus enabling removal of the cap from the beer keg.
Australian Patent Application No. 42201/85 discloses a similar cap to that of U.S. Pat. No. 4,779,750.
Often, pull tabs of the prior art are difficult to grasp with a user's fingers, do not tear the cap as desired to cause removal of the cap and/or break-off mid-way through the pulling action, thereby rendering the cap difficult to, and in some cases not, removable.
With regard to a beer keg cap disclosed in U.S. Pat. No. 4,779,750, in particular, problems have been encountered in the use of the cap.
Many brewing companies utilise automation techniques in filling beer kegs and providing a keg cap or seal on the filled keg. It has been found that due to the openness of the exposed pull tab of U.S. Pat. No. 4,779,750, interlocking of two caps can occur in a hopper feeding the automatic keg capping machinery. This may cause a blockage in the feeding hopper. Alternatively, parts of the interlocked caps may lead to undesirable fracture and separation as the caps are disengaged.
Furthermore, due to the overall design of the cap and the material from which the cap is manufactured, when the pull tab is pulled, the majority of the cap does not always separate into two halves. The pull tab itself may break in half, thus rendering removal of the cap more difficult. Breakage of the cap into a number of pieces may also create a litter problem.
Additionally, the cap disclosed in U.S. Pat. No. 4,779,750 uses a plurality of tear lines to define the pull tab. Upon pulling the tab, extra force must be exerted in order to fracture at least two lines of weakness. This extra force, in turn, may lead to a breakage of the pull tab itself, rather than separation of the cap from the keg.